This invention relates to a rotary encoder in which an optical element is used, and more particularly to a manually operable optical rotary encoder for use with a mode change-over switch of a video tape recorder (VTR), a manual input device for a numerically controlled machine tool, or the like.
Conventionally, for example in a VTR, when the machine is to be set to one of various ordinary modes such as rewinding, quick feeding, playback, and stopping of a tape, a mode change-over switch is operated to select a signal for a corresponding one of such individual modes. As a result, the selected control signal having a predetermined period is supplied to a motor to drive a tape to run in a direction and at a speed determined in accordance with the mode.
Various types of switches have been proposed for such a mode change-over switch as described above and put into practical use. However, in consideration of durability and reduced production of noises, it is advantageous to use an optical rotary encoder which is of the contactless type.
An example of an optical rotary encoder will be described with reference to FIGS. 4 and 5. An optical rotary encoder shown includes a code plate 1 on a surface of which light reflective portions 1a and non-reflective portions 1b are formed radially in a circumferentially equidistantly spaced relationship. The code plate 1 is secured to a supporting portion 2a of a support member 2, and the support member 2 has an enlarged diameter portion 2b formed below the supporting portion 2a thereof. The code plate 1 and the support member 2 are secured to a manually operable shaft 3. A plurality of notches or serrations 5 are formed on a circumferential periphery of the enlarged diameter portion 2b of the support member 2, and a ball 6 is urged into engagement with one of the notches 5 of the support member 2 by an urging device 4. The urging device 4 is secured to a stationary portion of an apparatus to which the optical rotary encoder is applied and on which the manually operable shaft 3 is mounted for manual rotation. The urging device 4 includes a cylindrical body 4a and a spring 7 accommodated in the cylindrical body 4a for pressing the ball 4 against the notched 5 periphery of the support member 2. A light emitting element 8 and a light receiving element 9 are located in an opposing relationship to the code plate 1. The notched 5 periphery of the support member 2, the ball 6 and the urging device 4 cooperatively constitute a click mechanism 10.
In the prior art device, if the manually operable shaft 3 is rotated relative to the urging device 4, the support member 2 secured to the manually operable shaft 3 is rotated together with the code plate 1. Meanwhile, an incident beam of light a from the light emitting element 8 which irradiates on a surface of the code plate 1 is reflected successively and alternately by the light reflective portions 1a and the non-reflective portions 1b of the code plate 1, and such reflective light b which exhibits changes in quantity of light between a high level and a low level now irradiates on the light receiving element 9. Accordingly, as the code plate 1 rotates a certain amount, the light receiving element 9 will produce a series of pulse signals. Since rotation of the manually operable shaft 3 corresponds to such various operation modes of a VTR as described above, a difference in number of pulses produced and determined by rotation of the manually operable shaft 3 can be used as a mode change-over signal.
However, in such a prior art device as described above, for example if rotation of the manually operable shaft 3 is stopped in a condition in which the beam of light a is incident to a light reflective portion 1a of the code plate 1, the light receiving element 9 will not produce accurate pulse signals. To eliminate this, the click mechanism 10 is provided to assure production of desired pulse signals at any of the predetermined positions with good reproducibility even by manual operation. Due to the presence of the click mechanism 10, as the manually operable shaft 3 is rotated, it can be clickably moved so that it may be stopped at a desired rotational position.
However, the ball 6 of the click mechanism 10 and the urging device 4 are separate from the support member 2 for the code plate 1 and are located adjacent a side of the support member 2. Therefore, it is necessary to position the click mechanism 10 relative to the code plate 1. Accordingly, it is a drawback of the prior art device that assemblage of the device involves complicated operations.